1. Field of the Invention
This invention relates to a vacuum valve device, and more particularly to a mold vacuum valve device for automatically obstructing discharge of molten material and air.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional mold vacuum valve device 8 disclosed in Taiwanese Patent No. 201231189 includes a first mold unit 81, a second mold unit 82, and a sliding block unit 83.
The first mold unit 81 includes a first mold body 811 and two resilient members 812. The first mold body 811 has a curved sliding surface 813 facing toward the second mold unit 82, a runner passage 814 and a vacuum passage 815. The runner passage 814 and the vacuum passage 815 are formed respectively in two opposite lateral sides of the first mold body 811. The sliding surface 813 is formed with position limiting groove 816. The first mold body 811 further has two holes 817 each extending along a direction parallel to the vacuum passage 815 and receiving the corresponding resilient member 812.
The second mold unit 82 includes a second mold body 821 having a serrated side surface 822 that faces toward the sliding block unit 83 and that is formed with a plurality of teeth 823. The serrated side surface 822 cooperates with the curved sliding surface 813 to define an accommodating space (I).
The sliding block unit 83 includes a sliding block 831, a plurality of balls 832, a roller 833, and two adjustment bolts 834. The sliding block 831 is disposed movably in the accommodating space (I), has a toothed portion 835 complementary to the serrated side surface 822 to define a shaping clearance (II) therebetween, and is movable on the curved sliding surface 813 along a direction parallel to the teeth 623. The shaping clearance (II) has two opposite ends in fluid communication with the runner passage 814 and the vacuum passage 815, respectively. The sliding block 831 further includes two restricting grooves 836 each receiving a plurality of the balls 832 to facilitate smooth movement of the sliding block 831 on the curved sliding surface 813, and a position-limiting protrusion 837 disposed on the restricting grooves 836 and engaging the position-limiting groove 816 in the first mold body 811. The roller 833 is disposed rotatably on a middle portion of the position-limiting protrusion 837 for contact with a wall of the first mold body 811 defining the position-limiting groove 816. The position-limiting protrusion 837 is biased by the resilient member 812 such that the sliding block 831 is moved toward the runner passage 814, and is formed with two threaded holes 838. The adjustment bolts 834 are engaged respectively into the threaded holes 838, and abut against the wall of the first mold body 811 defining the position-limiting groove 816. The adjustment bolts 834 are rotatable relative to the threaded holes 838 to adjust the size of the shaping clearance (II).
As such, when molten material flows into the accommodating space (I) through the runner passage 814, the sliding block 831 can be moved by the molten material to close the vacuum passage 815.
However, the aforesaid conventional mold vacuum valve device 8 suffers from the following disadvantages:
1. Since the position-limiting groove 816 and the position-limiting protrusion 837 are L-shaped, two retaining blocks 84 are needed to confine the sliding block unit 83 within the position-limiting groove 816. Consequently, the number of the components of the mold vacuum valve device 8 is increased, thereby resulting in an increase in the manufacturing cost and the assembly cost.
2. Since the sliding surface 813 is curved, a resistance to movement of the sliding block 831 on the sliding surface 813 is increased. Consequently, the sliding block 831 cannot move smoothly.